1. Field of the Invention
The invention relates to calcium-binding photoproteins, genes encoding the same, and use thereof.
2. Related Art
Calcium-binding photoproteins are photoproteins in which an apoprotein and a peroxide of a light-emitting substrate exist in the state of a complex formed therefrom. Calcium-binding photoproteins have the quality of momentarily emitting light on bonding with a calcium ion.
Known calcium-binding photoproteins include aequorin, obelin, clytin, mitrocomin, mineopsin and bervoin. Of these, aequorin is a typical calcium-binding photoprotein, the higher-order structure and light-emitting mechanism of which have been reported in detail (see, for example, Inouye et al., Proc. Natl. Acad. Sci. USA, 82, 3154-3158 (1985); Head et al., Nature, 405, 372-376 (2000)). Due to aequorin having a very high sensitivity to calcium ions, it is used to detect and assay trace amounts of calcium ions, and to measure changes in the intracellular concentration of calcium ions.
Clytin is a calcium-binding photoprotein obtained from the luminescent jellyfish Clytia gregarium (see Inouye, S. and Tsuji, F. I., FEBS Lett., 315, 343-346 (1993). Clytin exists in the state of a complex formed from apoclytin and a peroxide of the light-emitting substrate coelenterazine. When clytin bonds with a calcium ion, it momentarily emits light and forms coelenteramide—an oxide of coelenterazine, and carbon dioxide.